Slappy strokes. They're causing you a bunch of problems:
1. You're standing way behind the baseline to receive medium paced balls. If you were to stand in closer, where you should be standing, I'll bet you'd spray a lot of shots.
2. You're still spraying shots.
3. You're not putting enough topspin on the ball and are relying on a combination of low net clearance and gravity to keep your shots in the court.
Start with this http://www.youtube.com/watch?v=5ot2xQJRJ5Q
and then you can work on adding more power and spin.